How to Fix a Running Toilet?

Why It Matters

A running toilet can waste 200+ gallons of water per day — that's $50-$100 per month on your water bill. The good news is it's one of the easiest plumbing fixes, and the parts are cheap.

Step 1: Open the Tank and Diagnose

Take the lid off the back of the toilet tank. Flush and watch what happens. You're looking for one of three things:

Is Water Flowing Past the Flapper?

The flapper is the rubber disc at the bottom of the tank that seals the flush valve. When you flush, it lifts to release water into the bowl, then falls back down to seal.

Test: Push down on the flapper with your finger. If the running stops, the flapper isn't sealing properly.

Why it fails: Flappers deteriorate over time — chlorine in the water, minerals, and age cause the rubber to warp, harden, or grow buildup on the sealing surface.

Is the Fill Valve Not Shutting Off?

The fill valve is the tall mechanism on the left side of the tank. After a flush, it refills the tank and is supposed to shut off when the water reaches the correct level.

Test: If the water in the tank is overflowing into the overflow tube (the tall open pipe in the center of the tank), the fill valve isn't shutting off or the float is set too high.

Is Water Going Into the Overflow Tube?

Look at the water level. It should be about 1 inch below the top of the overflow tube. If water is continuously trickling into the overflow tube, your float level is set too high.

Fix #1: Replace the Flapper (Most Common — $3-$8)

1. Turn off the water supply valve (the knob on the wall behind the toilet)
2. Flush to empty the tank
3. Unhook the old flapper from the two pegs on either side of the flush valve
4. Disconnect the chain from the flush handle
5. Take the old flapper to the hardware store to match the size and style
6. Hook the new flapper on, connect the chain (should have about 1/2 inch of slack), and turn the water back on

Fix #2: Adjust the Float ($0 — Just an Adjustment)

If water is going into the overflow tube, the water level is too high.

For a ball float (older toilets): Bend the metal arm slightly downward. This lowers the float position and makes the fill valve shut off sooner.

For an integrated float (newer toilets): There's usually a screw or clip on the fill valve that adjusts the float height. Turn it clockwise (or slide the clip down) to lower the water level.

Target level: About 1 inch below the top of the overflow tube. Mark it with a pencil if it helps.

Fix #3: Replace the Fill Valve ($8-$15)

If the fill valve is old, corroded, or won't shut off even with proper float adjustment, replace the whole thing. Universal fill valves fit most toilets.

1. Turn off the water supply and flush to empty the tank
2. Place a towel under the tank — some water will drip
3. Disconnect the water supply line from the bottom of the tank (use pliers, turn counterclockwise)
4. Unscrew the lock nut on the bottom of the fill valve (inside the tank, it's the nut at the base of the fill valve)
5. Pull the old fill valve out from the top
6. Adjust the new fill valve to the correct height (follow the instructions on the box)
7. Drop it in, tighten the lock nut from below, reconnect the supply line
8. Turn the water on and adjust the float to the correct level

The Nuclear Option: Replace Everything at Once

If your toilet is over 10 years old and you're not sure which part is the problem, buy a complete toilet repair kit ($15-$25) and replace the flapper, fill valve, and supply line all at once. It takes 30 minutes and you won't have to think about it again for years.

When to Call a Professional

• The toilet still runs after replacing the flapper and fill valve (rare — could be a cracked flush valve seat)
• You hear water running but can't figure out where it's coming from
• The shutoff valve behind the toilet is stuck or leaking
• The toilet itself is cracked or leaking at the base

Expect to pay: $100-$200 for a plumber to fix a running toilet (mostly labor, since the parts are cheap). Given that the DIY fix costs $5-$15, this is one of the best repairs to learn yourself.